If you mean "Rainbow Reef" the little snorkelling pool which is onsite at Aulani then I am pretty sure it is all ages. They do make them wear a life jacket and the water is colder than you might think. I am not sure about the masks but I am pretty sure they will let you wear your own (someone correct me if I am wrong on that) There is a surcharge for Rainbow Reef and it will be closed for refurb sometime between the late summer and late October.